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<p>作为开发人员,无论是前端还是后端,与数据库都要进行打交道.后端开发自然不必多说,而身为前端,起码应该知道数据库最基础的操作,SQL基本的增删改查语句等.本篇主要是在学习使用PHP操作数据库的过程中,整理的一些资料,方便日后复习.</p>
</blockquote>
<h2 id="一、数据库的创建"><a href="#一、数据库的创建" class="headerlink" title="一、数据库的创建"></a>一、数据库的创建</h2><h3 id="1、创建数据库"><a href="#1、创建数据库" class="headerlink" title="1、创建数据库"></a>1、创建数据库</h3><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token comment">//创建数据库</span>
<span class="token variable">$createDb</span> <span class="token operator">=</span> <span class="token string double-quoted-string">"CREATE DATABASE database_name"</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>

<h3 id="2、检测数据库创建结果"><a href="#2、检测数据库创建结果" class="headerlink" title="2、检测数据库创建结果"></a>2、检测数据库创建结果</h3><h4 id="2-1、面向对象方法"><a href="#2-1、面向对象方法" class="headerlink" title="2.1、面向对象方法"></a>2.1、面向对象方法</h4><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token keyword">if</span><span class="token punctuation">(</span><span class="token variable">$conn</span> <span class="token operator">-&gt;</span> <span class="token function">query</span><span class="token punctuation">(</span><span class="token variable">$createDb</span><span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token constant boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"数据库创建成功！"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"Error creating database: "</span> <span class="token operator">.</span> <span class="token variable">$conn</span><span class="token operator">-&gt;</span><span class="token property">error</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h4 id="2-2、面向过程方法"><a href="#2-2、面向过程方法" class="headerlink" title="2.2、面向过程方法"></a>2.2、面向过程方法</h4><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">mysqli_query</span><span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token punctuation">,</span><span class="token variable">$createDb</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"数据库创建成功！"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"Error creating database: "</span> <span class="token operator">.</span> <span class="token function">mysqli_error</span><span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>


<h2 id="二、创建数据表"><a href="#二、创建数据表" class="headerlink" title="二、创建数据表"></a>二、创建数据表</h2><h3 id="1、创建表"><a href="#1、创建表" class="headerlink" title="1、创建表"></a>1、创建表</h3><blockquote>
<p>语法：<code>CREATE TABLE table_name();</code></p>
</blockquote>
<p><strong>实例</strong></p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token variable">$createTable</span> <span class="token operator">=</span> "<span class="token constant">CREATE</span> <span class="token constant">TABLE</span> <span class="token function">members</span> <span class="token punctuation">(</span>
id <span class="token keyword type-declaration">INT</span><span class="token punctuation">(</span><span class="token number">11</span><span class="token punctuation">)</span> <span class="token constant">UNSIGNED</span> <span class="token constant">AUTO_INCREMENT</span> <span class="token constant">PRIMARY</span> <span class="token constant">KEY</span><span class="token punctuation">,</span>
姓名 <span class="token function">VARCHAR</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span> <span class="token constant">NOT</span> <span class="token constant">NULL</span><span class="token punctuation">,</span>
电话 <span class="token function">VARCHAR</span><span class="token punctuation">(</span><span class="token number">13</span><span class="token punctuation">)</span> <span class="token constant">NOT</span> <span class="token constant">NULL</span><span class="token punctuation">,</span>
内容 <span class="token function">VARCHAR</span><span class="token punctuation">(</span><span class="token number">60</span><span class="token punctuation">)</span> <span class="token constant">NOT</span> <span class="token constant">NULL</span>
<span class="token punctuation">)</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p><strong>参数说明</strong></p>
<table>
<thead>
<tr>
<th>约束</th>
<th>说明</th>
</tr>
</thead>
<tbody><tr>
<td>NOT NULL</td>
<td>每一行都必须含有值（不能为空），null 值是不允许的。</td>
</tr>
<tr>
<td>DEFAULT</td>
<td>规定没有给列赋值时的默认值。</td>
</tr>
<tr>
<td>UNIQUE</td>
<td>保证某列的每行必须有唯一的值。</td>
</tr>
<tr>
<td>CHECK</td>
<td>保证列中的值符合指定的条件。</td>
</tr>
<tr>
<td>FOREIGN KEY</td>
<td>保证一个表中的数据匹配另一个表中的值的参照完整性。</td>
</tr>
<tr>
<td>PRIMARY KEY</td>
<td>NOT NULL 和 UNIQUE 的结合。确保某列（或两个列多个列的结合）有唯一标识，有助于更容易更快速地找到表中的一个特定的记录。</td>
</tr>
</tbody></table>
<h3 id="2、检测表的创建"><a href="#2、检测表的创建" class="headerlink" title="2、检测表的创建"></a>2、检测表的创建</h3><h4 id="2-1、面向对象方法-1"><a href="#2-1、面向对象方法-1" class="headerlink" title="2.1、面向对象方法"></a>2.1、面向对象方法</h4><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token keyword">if</span><span class="token punctuation">(</span><span class="token variable">$conn</span> <span class="token operator">-&gt;</span> <span class="token function">query</span><span class="token punctuation">(</span><span class="token variable">$createTable</span><span class="token punctuation">)</span><span class="token operator">===</span><span class="token constant boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"数据表创建成功&lt;br&gt;"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string single-quoted-string">'数据表创建错误：'</span> <span class="token operator">.</span><span class="token variable">$conn</span> <span class="token operator">-&gt;</span> <span class="token property">error</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h4 id="2-2、面向过程方法-1"><a href="#2-2、面向过程方法-1" class="headerlink" title="2.2、面向过程方法"></a>2.2、面向过程方法</h4><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">mysqli_query</span><span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token punctuation">,</span><span class="token variable">$createTable</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"数据表创建成功&lt;br&gt;"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string single-quoted-string">'数据表创建错误：'</span> <span class="token operator">.</span><span class="token function">mysqli_error</span><span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h3 id="3、向表中插入数据"><a href="#3、向表中插入数据" class="headerlink" title="3、向表中插入数据"></a>3、向表中插入数据</h3><p>在创建完数据表后，我们可以向表中插入数据，但须遵循一些语法规则：</p>
<ul>
<li>PHP 中 SQL 查询语句必须使用引号</li>
<li>在 SQL 查询语句中的字符串值必须加引号</li>
<li>数值的值不需要引号</li>
<li>NULL 值不需要引号</li>
</ul>
<h4 id="3-1、语法用法"><a href="#3-1、语法用法" class="headerlink" title="3.1、语法用法"></a>3.1、语法用法</h4><blockquote>
<p><strong>语法：</strong><br><code>INSERT INTO table_name (column1, column2, column3,...) VALUES (value1, value2, value3,...)</code></p>
</blockquote>
<p><strong>实例</strong></p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token operator">...</span>
<span class="token comment">//参照上方规则：字符串必须加引号</span>
<span class="token variable">$insertData</span> <span class="token operator">=</span> <span class="token string double-quoted-string">"INSERT INTO members (姓名,电话,内容)
VALUES ('"</span><span class="token operator">.</span><span class="token variable">$name</span><span class="token operator">.</span><span class="token string double-quoted-string">"',<span class="token interpolation"><span class="token variable">$phone</span></span>,'"</span><span class="token operator">.</span><span class="token variable">$comment</span><span class="token operator">.</span><span class="token string double-quoted-string">"')"</span><span class="token punctuation">;</span>

<span class="token operator">...</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h4 id="3-2、检测插入数据结果"><a href="#3-2、检测插入数据结果" class="headerlink" title="3.2、检测插入数据结果"></a>3.2、检测插入数据结果</h4><h5 id="3-2-1、面向对象方法"><a href="#3-2-1、面向对象方法" class="headerlink" title="3.2.1、面向对象方法"></a>3.2.1、面向对象方法</h5><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token operator">-&gt;</span><span class="token function">query</span><span class="token punctuation">(</span><span class="token variable">$insertData</span><span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token constant boolean">TRUE</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"新记录插入成功"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"Error: "</span> <span class="token operator">.</span> <span class="token variable">$insertData</span> <span class="token operator">.</span> <span class="token string double-quoted-string">"&lt;br&gt;"</span> <span class="token operator">.</span> <span class="token variable">$conn</span><span class="token operator">-&gt;</span><span class="token property">error</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h5 id="3-2-2、面向过程方法"><a href="#3-2-2、面向过程方法" class="headerlink" title="3.2.2、面向过程方法"></a>3.2.2、面向过程方法</h5><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">mysqli_query</span><span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token punctuation">,</span> <span class="token variable">$insertData</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"新记录插入成功"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"Error: "</span> <span class="token operator">.</span> <span class="token variable">$insertData</span> <span class="token operator">.</span> <span class="token string double-quoted-string">"&lt;br&gt;"</span> <span class="token operator">.</span>  <span class="token function">mysqli_error</span><span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h2 id="三、数据库连接"><a href="#三、数据库连接" class="headerlink" title="三、数据库连接"></a>三、数据库连接</h2><h3 id="1、面向对象方法"><a href="#1、面向对象方法" class="headerlink" title="1、面向对象方法"></a>1、面向对象方法</h3><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token comment">//数据库连接</span>
<span class="token variable">$conn</span> <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">mysqli</span><span class="token punctuation">(</span><span class="token variable">$servername</span><span class="token punctuation">,</span><span class="token variable">$username</span><span class="token punctuation">,</span><span class="token variable">$password</span><span class="token punctuation">,</span><span class="token variable">$database_name</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">//连接检测</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token variable">$conn</span> <span class="token operator">-&gt;</span> <span class="token property">connect_error</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">die</span><span class="token punctuation">(</span><span class="token string double-quoted-string">"Connection failed:"</span><span class="token operator">.</span><span class="token variable">$conn</span> <span class="token operator">-&gt;</span> <span class="token property">connect_error</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"数据库连接成功。&lt;br&gt;"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h3 id="2、面向过程方法"><a href="#2、面向过程方法" class="headerlink" title="2、面向过程方法"></a>2、面向过程方法</h3><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token comment">//数据库连接</span>
<span class="token variable">$conn</span> <span class="token operator">=</span> <span class="token function">mysqli_connect</span><span class="token punctuation">(</span><span class="token variable">$servername</span><span class="token punctuation">,</span><span class="token variable">$username</span><span class="token punctuation">,</span><span class="token variable">$password</span><span class="token punctuation">,</span><span class="token variable">$database_name</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">//检测连接</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token variable">$conn</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">die</span><span class="token punctuation">(</span><span class="token string double-quoted-string">"Connection failed: "</span> <span class="token operator">.</span><span class="token function">mysqli_connect_error</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string double-quoted-string">"数据库连接成功。"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="四、从数据库读取数据"><a href="#四、从数据库读取数据" class="headerlink" title="四、从数据库读取数据"></a>四、从数据库读取数据</h2><blockquote>
<p>语法：</p>
<ul>
<li><code>SELECT column_name(s) FROM table_name</code></li>
<li><code>SELECT * FROM table_name</code> 读取所有字段</li>
</ul>
</blockquote>
<h3 id="1、面向对象方法-1"><a href="#1、面向对象方法-1" class="headerlink" title="1、面向对象方法"></a>1、面向对象方法</h3><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token comment">//读取数据</span>
<span class="token variable">$fecth</span> <span class="token operator">=</span> <span class="token string double-quoted-string">"SELECT * FROM members"</span><span class="token punctuation">;</span>
<span class="token variable">$res</span> <span class="token operator">=</span> <span class="token variable">$conn</span> <span class="token operator">-&gt;</span> <span class="token function">query</span><span class="token punctuation">(</span><span class="token variable">$fecth</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">//检测读取结果并输出</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token variable">$res</span> <span class="token operator">-&gt;</span> <span class="token property">num_rows</span> <span class="token operator">&gt;</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword">while</span><span class="token punctuation">(</span><span class="token variable">$row</span> <span class="token operator">=</span> <span class="token variable">$res</span><span class="token operator">-&gt;</span><span class="token function">fetch_array</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string heredoc-string"><span class="token delimiter symbol"><span class="token punctuation">&lt;&lt;&lt;</span>HTML</span>
    &lt;div class="tbodyrow"&gt;
      &lt;span class="id tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"id"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
      &lt;span class="name tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"姓名"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
      &lt;span class="phone tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"电话"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
      &lt;span class="comment tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"内容"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
    &lt;/div&gt;
&lt;br&gt;
<span class="token delimiter symbol">HTML<span class="token punctuation">;</span></span></span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
<span class="token keyword">echo</span> <span class="token string double-quoted-string">"0结果"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h3 id="2、面向过程方法-1"><a href="#2、面向过程方法-1" class="headerlink" title="2、面向过程方法"></a>2、面向过程方法</h3><pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token comment">//读取数据</span>
<span class="token variable">$fecth</span> <span class="token operator">=</span> <span class="token string double-quoted-string">"SELECT * FROM members"</span><span class="token punctuation">;</span>
<span class="token variable">$res</span> <span class="token operator">=</span> <span class="token function">mysqli_query</span><span class="token punctuation">(</span><span class="token variable">$conn</span><span class="token punctuation">,</span><span class="token variable">$fecth</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">//检测读取结果并输出</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">mysqli_num_rows</span><span class="token punctuation">(</span><span class="token variable">$res</span><span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword">while</span><span class="token punctuation">(</span><span class="token variable">$row</span> <span class="token operator">=</span> <span class="token function">mysqli_fetch_array</span><span class="token punctuation">(</span><span class="token variable">$res</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">echo</span> <span class="token string heredoc-string"><span class="token delimiter symbol"><span class="token punctuation">&lt;&lt;&lt;</span>HTML</span>
    &lt;div class="tbodyrow"&gt;
      &lt;span class="id tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"id"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
      &lt;span class="name tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"姓名"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
      &lt;span class="phone tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"电话"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
      &lt;span class="comment tbody"&gt;<span class="token interpolation"><span class="token punctuation">{</span><span class="token variable">$row</span><span class="token punctuation">[</span><span class="token string double-quoted-string">"内容"</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span>&lt;/span&gt;
    &lt;/div&gt;
&lt;br&gt;
<span class="token delimiter symbol">HTML<span class="token punctuation">;</span></span></span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
<span class="token keyword">echo</span> <span class="token string double-quoted-string">"0结果"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h3 id="拓展"><a href="#拓展" class="headerlink" title="拓展"></a>拓展</h3><h4 id="1、WHERE"><a href="#1、WHERE" class="headerlink" title="1、WHERE"></a>1、WHERE</h4><blockquote>
<p>WHERE 子句用于提取满足指定标准的的记录。</p>
</blockquote>
<p><strong>语法：</strong></p>
<pre class="line-numbers language-none"><code class="language-none">SELECT column_name(s) 
FROM table_name
WHERE column_name operator value<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>

<p><strong>实例</strong></p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token variable">$where</span> <span class="token operator">=</span> <span class="token string double-quoted-string">"SELECT * FROM members WHERE 姓名='张三' "</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre>

<h4 id="2、ORDER-BY"><a href="#2、ORDER-BY" class="headerlink" title="2、ORDER BY"></a>2、ORDER BY</h4><blockquote>
<p>ORDER BY 关键词用于对记录集中的数据进行排序。<br>默认升序排序，可以使用 DESC 进行降序排序。</p>
</blockquote>
<p><strong>语法：</strong></p>
<pre class="line-numbers language-none"><code class="language-none">SELECT column_name(s)
FROM table_name
ORDER BY column_name(s) ASC|DESC<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>

<p><strong>实例</strong></p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token variable">$order</span> <span class="token operator">=</span> "<span class="token constant">SELECT</span> <span class="token operator">*</span> <span class="token constant">FROM</span> members <span class="token constant">ORDER</span> <span class="token constant">BY</span> id <span class="token constant">DESC</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre>

<p><strong>根据两列进行排序</strong></p>
<p>可以根据多个列进行排序。当按照多个列进行排序时，只有第一列的值相同时才使用第二列：</p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token constant">SELECT</span> <span class="token function">column_name</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span>
<span class="token constant">FROM</span> table_name
<span class="token constant">ORDER</span> <span class="token constant">BY</span> column1<span class="token punctuation">,</span> column2<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>

<p><strong>特殊：拼音排序</strong></p>
<p>拼音排序需要根据字符集采用的编码决定使用方法</p>
<table>
<thead>
<tr>
<th>字符集</th>
<th>使用方法</th>
</tr>
</thead>
<tbody><tr>
<td>gbk (中文编码)</td>
<td>直接在查询语句后边添加 <code>ORDER BY</code></td>
</tr>
<tr>
<td>utf8 (万国码)</td>
<td>先对字段进行转码然后排序。<br>方法：<code>CONVERT(row_title using gbk)</code></td>
</tr>
</tbody></table>
<p>实例：现有表格如下。对表格按姓名拼音排序</p>
<table>
<thead>
<tr>
<th>id</th>
<th>姓名</th>
<th>性别</th>
</tr>
</thead>
<tbody><tr>
<td>1</td>
<td>丁一</td>
<td>女</td>
</tr>
<tr>
<td>2</td>
<td>牛二</td>
<td>男</td>
</tr>
<tr>
<td>3</td>
<td>张三</td>
<td>男</td>
</tr>
</tbody></table>
<p>执行操作(由于原本是拼音升序，所以这里我们用降序来区别)</p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token variable">$orderPy</span> <span class="token operator">=</span> <span class="token string double-quoted-string">"SELECT * FROM members
ORDER BY CONVERT(姓名 using gbk) DESC"</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<p>输出结果：</p>
<table>
<thead>
<tr>
<th>id</th>
<th>姓名</th>
<th>性别</th>
</tr>
</thead>
<tbody><tr>
<td>3</td>
<td>张三</td>
<td>男</td>
</tr>
<tr>
<td>2</td>
<td>牛二</td>
<td>男</td>
</tr>
<tr>
<td>1</td>
<td>丁一</td>
<td>女</td>
</tr>
</tbody></table>
<h4 id="3、UPDATE"><a href="#3、UPDATE" class="headerlink" title="3、UPDATE"></a>3、UPDATE</h4><blockquote>
<p>UPDATE 语句用于更新数据库表中已存在的记录。</p>
</blockquote>
<p><strong>语法：</strong></p>
<pre class="line-numbers language-none"><code class="language-none">UPDATE table_name
SET column1=value, column2=value2,...
WHERE some_column=some_value<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>
<blockquote>
<p>注意：UPDATE 语法中的 WHERE 子句。WHERE 子句规定了哪些记录需要更新。如果您想省去 WHERE 子句，所有的记录都会被更新！</p>
</blockquote>
<p><strong>实例</strong></p>
<p>现有如下表格：（已设置降序排列）</p>
<table>
<thead>
<tr>
<th>id</th>
<th>姓名</th>
<th>电话</th>
<th>内容</th>
</tr>
</thead>
<tbody><tr>
<td>3</td>
<td>张三</td>
<td>333</td>
<td>我叫张三</td>
</tr>
<tr>
<td>2</td>
<td>牛二</td>
<td>222</td>
<td>我叫牛二</td>
</tr>
<tr>
<td>1</td>
<td>丁一</td>
<td>111</td>
<td>我叫丁一</td>
</tr>
</tbody></table>
<p>修改更新表中 张三 为 李四</p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token variable">$updateData</span> <span class="token operator">=</span> "<span class="token constant">UPDATE</span> members <span class="token constant">SET</span> 姓名<span class="token operator">=</span><span class="token string single-quoted-string">'李四'</span>
<span class="token constant">WHERE</span> 姓名 <span class="token operator">=</span> <span class="token string single-quoted-string">'张三'</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>
<p>输出结果</p>
<table>
<thead>
<tr>
<th>id</th>
<th>姓名</th>
<th>电话</th>
<th>内容</th>
</tr>
</thead>
<tbody><tr>
<td>3</td>
<td>李四</td>
<td>333</td>
<td>我叫张三</td>
</tr>
<tr>
<td>2</td>
<td>牛二</td>
<td>222</td>
<td>我叫牛二</td>
</tr>
<tr>
<td>1</td>
<td>丁一</td>
<td>111</td>
<td>我叫丁一</td>
</tr>
</tbody></table>
<p><strong>UPDATE方法可以同时修改一条数据的多个字段</strong></p>
<p>修改更新表中</p>
<ul>
<li>张三 ——&gt; 李四</li>
<li>333 ——&gt; 444</li>
<li>我叫张三 ——&gt; 我叫李四</li>
</ul>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token variable">$updateData</span> <span class="token operator">=</span> "<span class="token constant">UPDATE</span> members <span class="token constant">SET</span> 
姓名<span class="token operator">=</span><span class="token string single-quoted-string">'李四'</span><span class="token punctuation">,</span>电话 <span class="token operator">=</span> <span class="token string single-quoted-string">'444'</span><span class="token punctuation">,</span> 内容 <span class="token operator">=</span> <span class="token string single-quoted-string">'我叫李四'</span>
<span class="token constant">WHERE</span> 姓名 <span class="token operator">=</span> <span class="token string single-quoted-string">'张三'</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>

<p>输出结果：</p>
<table>
<thead>
<tr>
<th>id</th>
<th>姓名</th>
<th>电话</th>
<th>内容</th>
</tr>
</thead>
<tbody><tr>
<td>3</td>
<td>李四</td>
<td>444</td>
<td>我叫李四</td>
</tr>
<tr>
<td>2</td>
<td>牛二</td>
<td>222</td>
<td>我叫牛二</td>
</tr>
<tr>
<td>1</td>
<td>丁一</td>
<td>111</td>
<td>我叫丁一</td>
</tr>
</tbody></table>
<blockquote>
<p>id设置为 <code>PRIMARY KEY</code>,不要轻易去改变它,若需要改变，不可与已存在的重复，否则无法更新数据。</p>
</blockquote>
<h4 id="4、DELETE"><a href="#4、DELETE" class="headerlink" title="4、DELETE"></a>4、DELETE</h4><blockquote>
<p>DELETE 语句用于从数据库表中<strong>删除行</strong>。</p>
</blockquote>
<p><strong>语法：</strong></p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token constant">DELETE</span> <span class="token constant">FROM</span> table_name
<span class="token constant">WHERE</span> some_column <span class="token operator">=</span> some_value<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>

<blockquote>
<p>注意：DELETE中的WHERE子句。WHERE 子句规定了哪些记录需要删除。如果您想省去 WHERE 子句，所有的记录都会被删除！</p>
</blockquote>
<p><strong>实例</strong></p>
<p>现有表格同上，需要删除id为3的行：</p>
<pre class="line-numbers language-php" data-language="php"><code class="language-php"><span class="token variable">$delete</span> <span class="token operator">=</span> " <span class="token constant">DELETE</span> <span class="token constant">FROM</span> members
<span class="token constant">WHERE</span> 姓名 <span class="token operator">=</span> <span class="token string single-quoted-string">'李四'</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>

<p>输出结果：</p>
<table>
<thead>
<tr>
<th>id</th>
<th>姓名</th>
<th>电话</th>
<th>内容</th>
</tr>
</thead>
<tbody><tr>
<td>2</td>
<td>牛二</td>
<td>222</td>
<td>我叫牛二</td>
</tr>
<tr>
<td>1</td>
<td>丁一</td>
<td>111</td>
<td>我叫丁一</td>
</tr>
</tbody></table>
<p><code>drop</code> <code>truncate</code>和 <code>delete</code>都可以对数据表进行删除操作，具体区别如下表：</p>
<table>
<thead>
<tr>
<th>语句</th>
<th>含义</th>
</tr>
</thead>
<tbody><tr>
<td>drop</td>
<td><strong>删除表</strong>。删除表及其结构。<strong>不可回滚</strong></td>
</tr>
<tr>
<td>truncate</td>
<td><strong>清空表</strong>。删除表中所有数据，保留表结构。<strong>不可回滚</strong></td>
</tr>
<tr>
<td>delete</td>
<td><strong>删除行</strong>。删除操作作为事务记录在日志中。<strong>可以回滚</strong></td>
</tr>
</tbody></table>
<blockquote>
<p><code>TRUNCATE</code>与不带 <code>WHERE</code> 的 <code>DELETE</code> 都是删除表数据，保留表结构。</p>
</blockquote>

                
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